Upon divestiture of the Bell Operating Companies from the American Telephone & Telegraph Company a demarcation point between an incoming telephone line and the interconnected subscriber premises line is to be provided at the subscriber premises. The demarcation point is to facilitate determination of whether a fault exists on the incoming telephone line or the subscriber premises line.
Typically, since divestiture, the demarcation point is provided by prior art telephone network interface apparatus mounted at the subscriber premises which includes a housing providing respective telephone company and subscriber compartments for mounting the respective telephone company and subscriber terminals, and other respective equipment, separate doors or covers for securing the respective compartments, and a telephone jack for connection to the incoming telephone line and a telephone plug for connection to the subscriber premises line. Upon the telephone jack and plug being connected to such lines, the telephone plug being plugged into the telephone jack, and a telephone being connected to the subscriber premises line, the telephone is rendered operable. Should the telephone become inoperable, the telephone plug is unplugged from the telephone jack and to provide the demarcation point and permit the plug of an operating telephone to be plugged into the jack to facilitate determination of whether a fault exists on the incoming telephone line or the subscriber premises lines, i.e. upon the plug of an operating telephone being plugged into the telephone jack and the telephone operating, the fault is determined to be on the subscriber premises line, however, upon the telephone not operating, the fault is determined to be on the incoming telephone line. Representative of such prior art telephone network interface apparatus or devices are those disclosed in U.S. Pat. Nos. 4,488,008 for TELEPHONE NETWORK INTERFACE DEVICE patented Dec. 11, 1984; 4,500,158 for NETWORK INTERFACE DEVICE patented Feb. 19, 1985; and 4,647,725 for INDOOR TYPE TELEPHONE NETWORK INTERFACE DEVICE patented Mar. 3, 1987.
Generally, such prior art telephone network interface apparatus are particularly useful, and economically feasible, at subscriber premises where only a relatively small number, e.g. 1, 2, 4, etc., of incoming telephone lines and subscriber premises lines are interconnected. However, at divestiture, the telephone network system throughout the country was, and largely still is, replete with 25, 50, etc. multi-line or pair telephone terminal blocks previously mounted or installed at various subscriber premises such as office buildings, condos, apartments, etc., for terminating or electrically interconnecting large numbers e.g. 25, 50, etc., of incoming telephone lines with an equally large number of subscriber premises lines. An example of such multi-line telephone terminal blocks is illustrated in FIG. 1 and identified by general numberical designation 10. Block 10 is typically mounted vertically at a multi-line subscriber premises and will be presumed to be for purposes of explanation a vertically mounted 50 line or pair telephone terminal block referred to in the art as the 66 block. Such 66 block 10 is provided with two vertically oriented parallel rows 12 and 14 of 25 pair each, e.g. pairs 16, 18, 20 and 22, of electrically conductive telephone terminals for electrically terminating or interconnecting 50 incoming telephone lines from a telephone central office 24 with 50 subscriber premises lines, e.g., pair of telephone terminals 16 electrically interconnect incoming telephone line 26 with subscriber premises line 28 connected to subscriber telephone 30 and pair of telephone terminals 20 electrically interconnect incoming telephone line 32 with subscriber premises line 34 connected to subscriber telephone 36. It will be noted from FIG. 1 that pair of telephone terminals 16 from row 12 and pair of telephone terminals 20 from row 14 are displaced horiziontally on the telephone terminal block 10 with respect to each other and that the telephone terminals of each pair, e.g. telephone terminals 38 and 39 of pair 20 (lower righthand corner of FIG. 1) are displaced vertically with respect to each other and that each telephone terminal, e.g. telephone terminal 39, is provided with a pair of prongs 41 and 42 displaced horizontally with respect to each other and extending outwardly from the telephone terminal block 10. As may be noted by referring to the upper portion of FIG. 1, and pairs of telephone terminals 16 and 20, the inner prongs of each pair are typically electrically connected to the incoming telephone lines (e.g. incoming telephone lines 26 and 32) and the outer prongs of each pair are connected to the subscriber premises lines, e.g. subscriber premises lines 28 and 34. It will be further understood that the telephone terminal block 10 is made of a suitable electrically insulating material and that only the prongs of the telephone terminal extend outwardly from the telephone block with the interconnecting portions being typically embedded within the telephone terminal block. Still further, it will be understood that each incoming telephone line and each subscriber premises line is comprised of two electrical conductors typically referred to in the art as tip T and ring R as illustrated in FIG. 1.
Typically, the previously mounted multi-line telephone terminal blocks are without means to provide the needed e.g. 25, 50, etc., demarcation points between the incoming telephone lines and the interconnected subscriber premises lines; the 66 block 10 of FIG. 1 requires, for example, means for providing 50 demarcation points between the 50 incoming telephone lines and the 50 subscriber premises lines interconnected at the block. The typical size of the above-noted prior art telephone network interface apparatus is such that they are too large to be mounted on such previously mounted multi-line telephone terminal blocks, e.g. 66 block 10, and the typical cost of such telephone network interface apparatus is such that they are too expensive to provide the needed large number, e.g. 25, 50, etc., of demarcation points.
Accordingly there exists a need in the telephone network interface system art for retrofit apparatus for retrofitting these previously mounted telephone multi-line telephone terminal blocks to provide them with such large number of needed demarcation points.
Further, for present market acceptability, it is believed to be desirable to provide such needed retrofit apparatus utilizing presently available, so-called standard, RJ-11 telephone plug and jack, or at least equivalent structure of the RJ-11 jack. However, the width of such RJ-11 telephone plug, and the width of the space typically available on these previously mounted multi-line telephone terminal blocks for mounting the needed retrofit apparatus supporting the RJ-11 jack or its equivalent, are such that a difficult problem is presented as will be better understood by reference to FIG. 2. [It will be understood that since the subscriber line extending from a subscriber's telephone terminates in a telephone plug, typically the standard RJ-11 telephone plug the telephone jack comprising the demarcation point must be connected to the incoming telephone line and hence such jack must be mounted on the retrofit apparatus and for present market acceptability desirably is an RJ-11 telephone jack or the equivalent structure for receiving the RJ-11 telephone plug.] More specifically, the width W1 (FIG. 2) of such RJ-11 telephone plug 40 is approximately 0.380 inch and the width W2 of the space available on multi-line telephone terminal block 10 between pairs of telephone terminals, e.g. 42, 43, 44 and 45 in a vertical row thereof, for mounting the needed retrofit apparatus, and hence the width available for mounting the RJ-11 jack or its equivalent structure, is typically only approximately 0.400 inch leaving only approximately 0.020 inch available for the opposed walls of the telephone jack or its equivalent structure plus clearance between adjacently mounted retrofit apparatus. This means that, with clearance, the width of each opposed wall of the telephone jack or its equivalent structure, must be less than approximately 0.010 inch, and considering the realities of present economically feasible manufacture, such wall thickness is too small for realistic consideration. Thus it has been discovered that to mount a plurality of such retrofit apparatus adjacently on such previously mounted multi-line telephone terminal block to provide the large number of needed demarcation points, the opposed walls of the telephone jack, or the equivalent structure, must be open. This means that a telephone plug plugged into such open wall telephone jack is unprotected from disturbance, e.g. unintentional unplugging due to the intentional unplugging of adjacent telephone plugs from the telephone jacks of adjacent retrofit apparatus, jostling of the telephone plug sufficient to interrupt the connection provided by the telephone plug between an incoming telephone line and a subscriber premises line, etc.
Accordingly, there exists a further need in the art for providing such retrofit apparatus wherein a telephone plug plugged into such open walled telephone jack is free, or at least substantially free, from such disturbance.